1. Field of the Invention
The present invention relates to a heat transfer measurement method and system. More particularly, the present invention relates to a method and system for measuring heat transfer in a transient environment, using a hybrid of active and passive techniques.
2. Description of Related Art
Though temperature measurements have long been used to study the flow of thermal energy in the design and optimization of heating and cooling systems, temperature is only a secondary variable. A complete understanding of the heat transfer profile in an environment requires accurate measurement of the heat transfer rate. However, due to the complex nature of thermal energy flow, the heat transfer rate is an extremely difficult quantity to accurately measure. Generally, heat transfer measurement techniques are known in the art that employ either an active or passive technique, but not both.
The active technique involves measuring the amount of power required to maintain either a constant temperature or power output for a surface in a given environment. The heat transfer rate can be calculated by determining the temperature of the surface, the temperature in the environment, and the amount of power provided to the surface. However, this technique has some significant shortcomings. In particular, the active approach requires a large and bulky power supply to maintain constant temperature or power output of the surface under extreme temperature conditions. In addition, this technique requires a complex and expensive temperature controller to assure a constant temperature of the surface in the transient environment.
The other method known in the art is the passive approach. This method involves initially altering the temperature of a surface and allowing the surface to transiently equilibrate. Using the passive technique, the heat transfer rate can be calculated with knowledge of the initial and final temperatures of the surface, the environment temperature, and the time or history between the initial and final temperatures (i.e., the time for the temperature of the surface to equilibrate with the temperature of the environment). Although the passive technique does not require a large power source, it provides limited data acquisition time and can result in difficult quantitative interpretation.
In view of the foregoing, there is a need for an improved method and system for measuring heat transfer in an environment.